Two years ago this month, in a disused Norfolk airfield, a small group of scientists were preparing to undertake one of the more controversial experiments in British scientific history. What little equipment it needed – a B&Q pressure washer, 1km of hydraulic hose and an 8m air balloon – had been bought or loaned. A truck was ready. Once in the air, the dirigible balloon would spray 120 litres of fine water droplets into the East Anglia sky, a miniaturised test for a much larger system that would eventually pump out chemical particles to reflect sunlight and, so the scientists calculated, cool the planet. It was to be a momentous day.

Geoengineering – as defined by the Royal Society in 2009 – is the large-scale, technological manipulation of the climate (some call it “planet hacking”). After decades of theorising, the Cambridge group was going to be the first in the West to take research out of doors. But shortly before lift-off, they aborted. There was, they feared, no way of knowing who could use their research, or in what way, and the Stratospheric Particle Injection for Climate Engineering (Spice) team did not want to open a door that might be impossible to close.

Little has changed in practical terms since 2011. The Spice balloon has been shipped back to its owners; the pressure washer is back in use spraying down cars. Yet, since the end of last month, the prospect of geoengineering has cast a giant shadow over the world of environmental campaigners and climate scientists. On 27 September, the Intergovernmental Panel on Climate Change (IPCC), the world’s most respected authority on global warming, acknowledged for the first time the need to consider it as a weapon against rising temperatures.